Devices such as integrated circuits that have circuitry and/or structures for sensing a magnetic field should be tested by applying a known magnetic field and measuring an output signal to determine whether an actual output signal is sufficiently close to an expected output signal. One way to perform such testing is to use a coil in a bench test. This process allows testing in a carefully controlled testing environment, but is labor intensive and not suitable for testing large numbers of devices. It would be desirable to have a system that could automatically and controllably test large numbers of devices designed to sense magnetic fields, and more desirable to further be able to control for electrical and temperature effects.
A testing system according to the present invention tests devices in the presence of a magnetic field repeatably and quickly so that production runs of devices can be tested.
The testing system preferably also includes equipment for performing electrical testing, and is configured so that both electrical input and magnetic input can be provided at one testing location. A magnetic field source, preferably an electromagnetic coil that allows the magnetic field to be controlled and varied to test at multiple known magnitudes, provides a known magnetic field to a device with a magnetic core assembly. The core assembly is integrated into the testing machine in such a way that the magnetic flux is contained but can be passed directly through the device being tested. This containment is accomplished by the configuration of the core assembly and the selection of materials, depending on whether those materials have high permeability or low permeability.
Because of the use of a magnetic field, components of the core assembly should have high permeability, e.g., a maximum D.C. permeability at least on the order of 105, while other components near the device and the core should have permeability close to one (1). Such low permeability materials include plastic and certain types of stainless steel (e.g., the 300 series). In addition, it is desirable for the track or conveyor to have a slit at a location near the device to minimize Lorentz forces that may be induced near the device when the magnetic field changes. This slit is particularly desirable if the magnetic generator is a coil and the magnetic field varies.
The system is preferably configured for surface mount SOIC packages or for dual in-line packages (DIPs).
In a method according to the present invention, a device is brought to a testing location, and electrical conductors are brought into contact with pins from the device to sense output signals in response to input conditions. One or more electrical signals are provided from the conductors to one or more of the pins, and a resulting signal or signals is/are sensed with the conductors in response to the electrical input. One or more known magnetic fields are applied to the device and a resulting signal or signals is/are sensed in response to the magnetic field input. These electrical and magnetic tests are performed sequentially in either order (although preferably magnetic last) while the device is held in one testing location. The method thus allows multiple tests to be performed without moving the device to another location between tests.
The testing system of the present invention can thus provide a controllable and variable magnetic field directly through the device and can contain the generated magnetic field over a wide range of field strengths. The testing system of the present invention can perform electrical and magnetic tests of integrated circuits quickly and at a single location, thus speeding the process per device. The testing system preferably also controls temperature, so the device can be characterized in a uniform temperature environment and over the full temperature range if desired. Other features and advantages will become apparent from the following detailed descriptions, drawings, and claims.